Forming means for profile grinding wheels



March 29, 1955 H. s. HALLEWELL 2,705,004

FORMING MEANS FOR PROFILE GRINDING WHEELS Filed Sept. 6, 1952 3Sheets-Sheet l m nwra/e A. s. HAM/P144624 March 29, 1955 H. s. HALLEWELLFORMING MEANS FOR PROFILE GRINDING WHEELS Filed Sept. 6, 1952 5Sheets-Sheet 2 JQuba March 29, 1955 s, HALLEWELL 2,705,004

FORMING MEANS FOR PROFILE GRINDING WHEELS Filed Sept. 6, 1952 I 3Sheets-Sheet 3 United States Patent FORMING MEANS FOR PROFILE GRINDINGWHEELS Harold Stuart Hallewell, Hillingdon Heath, England ApplicationSeptember 6, 1952, Serial No. 308,210

Claims priority, application Great Britain September 10, 1951 Claims.(Cl. 125-11) This invention relates to a pantographic wheel dressingdevice adapted to be attached to a grinding machine and employed forforming on the grinding wheel thereof a profile reproduced from atemplate, the device being of the kind having a base adapted to bemounted on the grinding machine, means for mounting the template in aplane, a template-follower member rockable about an axis perpendicularto the template plane and mounted in a bearing in a first member, adressing-tool holder rockable about an axis perpendicular to thetemplate plane and mounted in a bearing in a second member, a pantographconnection between said first and second members, and a connectionsupplementary to the pantograph connection for constraining thetemplate-follower member and the dressing-tool holder to rock in unison.

In devices of this kind at present in use the dressingtool is usually ofthe diamond-tipped chisel type, mounted in the dressing-tool holder sothat the axis of its tip, which is radiused, lies on the rocking axis ofthe holder. In operation, the grinding wheel being dressed is settangentially to the rocking axis of the dressing-tool holder.

Grinding machines are often used in the production of profiled toolssuchas lathe tools. Such a tool usually has the face in which the cuttingedge is formed relieved by at least a few degrees so that, except forthe cutting edge, the face clears the work. Therefore, when grinding aprofile on the tool, it is set in the grinding machine with its cuttingface inclined at the relief angle to a tangent to the grinding wheelsurface. It will be apparent that the profile (hereafter called thefirst profile) which is formed on the grinding wheel differs from, andis a distortion of, the profile (hereinafter called the second profile)which the tool forms on a workpiece. It will be apparent that the saidfirst profile must also be distorted when the tool is raked, sinceotherwise an accurate second profile is not obtained.

When the sum of the relief and rake angles is about 10 or less (accountbeing taken of the relative senses of the two angles) the first profilecan be produced on the grinding wheel, using a template profile of thesame form as the second profile, without introducing serious errors, bydisplacing the dressing-tool a predetermined short distance along thesaid rocking axis. This displacement is usually made in the direction inwhich the adjacent portion of the grinding wheel periphery -is moving,since if it were made in the reverse direction the dressing-tool mightbe drawn into the wheel and damaged or destroyed. The required magnitudeof the displacement can be calculated using well-known formulae.

For rake and relief angles, the sum of which is greater than 10, theerrors introduced by the above-mentioned method of producing the firstprofile become appreciable, and therefore the distortion must becompensated for by modifying the template profile. Even if the secondprofile is simple in form, the calculation of the modified form of thetemplate profile to give the required first profile can be a tedious andlengthy operation.

An object of this invention, therefore, is to provide a pantographicwheel-dressing device of the kind specified with which the said firstprofile can be formed on the grinding wheel of a grinding machine byusing a template profile of the same form as the said second profile.

According to this invention, the above object is attained by providingthat in a pantographic wheel dressing device of the kind specified, thepart of said means for supporting the template and to which the template2,705,004 Patented Mar. 29, 1955 "ice can be secured is tiltable aboutan axis which is disposed in parallelism or approximate parallelism tothe plane of the template, and which is adjustable to be capable ofbeing set parallel to the axis of rotation of the grinding wheel.

A typical operation for which grinding machines are used is theproduction of dies which subsequently are used for generating rolledscrew threads on bar stock. The dies may consist of flat rectangularplates and, during the rolling operation are moved relatively to oneanother in two spaced parallel planes with the member being rolleddisposed between them, the direction of movement being parallel to oneof the sides of the dies. With the abovementioned rectangular form ofdie, the ridges and grooves constituting the die profile are inclined atthe helix angle to its longer sides. During the grinding operation, thedie blank is so disposed that the grinding wheel traverses it in adirection parallel to the said ridges and grooves. It will be apparent,therefore, that the profile (hereinafter called the first profile),which must be formed on the grinding wheel by the dressing tool differsfrom, and is a distortion of the thread profile (hereafter called thesecond profile) which the dies form on the bar stock. This is due to thefact that the grooves are oblique to the sides of the die. Thisobliquity slightly affects the angularity of the sides of the groovesand requires the angles of the sides of the grooves to be compensatedtherefor so that in a direction of the sides of the dies the angles ofthe grooves will be proper for the threads being rolled. The angles ofthe sides of the threads in a direction normal to the direction ofmovement of the die must be 55 or 60 for standard screw threads. Asthese grooves are ground longitudinally the angles on the sides of thegrooves on the wheel must be slightly less than these standard threadangles.

Therefore, with the apparatus known hitherto, before such an operationcan be begun it is necessary to calculate the form of the first profile,i. e. the form which the second profile takes when rotated through thehelix angle about an axis in the plane of the profile and perpendicularto the grooved face of the die. The template profile has the same formas the first profile. Even if the second profile is simple in form thiscalculation can be a tedious and lengthy operation.

Another object of this invention is to provide a pantographicwheel-dressing device of the kind specified with which thelast-mentioned first profile can be formed on the grinding wheel of agrinding machine using a template profile of the same form as thelast-mentioned second profile.

Also according to this invention, the last-mentioned object is attainedby providing that in a pantographic wheel-dressing device of the kindspecified, the part of said means for supporting the template to whichthe template can be secured is rotatable about an axis, which isdisposed approximately parallel to and adjacent the plane of thetemplate, and which is capable of being set pehrpelndicular to the axisof rotation of the grinding w ee An embodiment of this invention willnow be described, by way of example, with reference to the accompanyingdrawings wherein:

Figs. 1A and 13 together show a front view in elevation of the completedevice,

Fig. 2 is a side view of part of the device, the view being partly invertical section and partly in elevation taken on broken line 2-2 inFig. 1A, and

Fig. 3 is a plan view of the part of the device shown in Fig. 2 with thetemplate and the template-follower member removed.

Referring now to Figs. 1A and 1B, the device includes a baseplate 10 towhich are fixed plates 11 adapted to be engaged by the magnetic chuck ofa grinding machine (not shown). The pantograph connection comprises alink parallelogram constituted by two short and two long links. Thefirst long arm of the link parallelogram comprises a more or lesshorizontal H-section link 12 pivoted to a more or less vertical shortlink 13 about a horizontal axis 14, which is fixed relatively to thebase 10 and thus constitutes the fixed point of the pantographconnection. The short link 13 constitutes the second arm of the linkparallelogram and is pivoted about the axis 14 to a mounting 15 on thebase plate.

A tubular lever 16 parallel to the short link 13 is pivoted to the freeend of the long link 12 at 17 and carries a template-follower pin 18 atits upper end. A light alloy casting 19 (Figs. 1A and 1B) constitutesthe third, long arm of the parallelogram extending parallel to the longlink 12, the casting being of inverted channel section with boxed-inends and serving to protect the bearings of the link parallelogram fromrust, etc. The casting is pivoted to the lever 16 about an axis 20 andto the short link 13 about an axis 21. The portion of the lever 16between the pivots 17 and 20 constitutes the fourth, short arm of theparallelogram.

The supplementary connection comprises three steel tapes 22, 23 and 24,the two tapes 22 and 23 both passing round and being pinned to theperiphery of a rotatable drum 25 coaxial with the axis 20, and eachpassing round and being pinned to the periphery of a different one oftwo drums 26 and 27 coaxial and rotatable with a dressing-tool holder 28and a shaft 29 (Fig. 2) respec tively. The third tape 24 passes roundand is pinned to the peripheries of two drums 30 and 31 coaxial androtatable with the shaft 29 and the template-follower pin 18respectively. Each tape is provided with a tensioning spring 32.

A bracket 33 (Fig. 2) rigid with the base 10 extends parallel to thelever 16 and carries a support to which a template can be fixed. Thesupport is formed in three separate parts, a part 34 rigid with thebracket 33, a part 35 hinged to the part 34 about a vertical axis AA,and a part 36 hinged to the part 35 about a horizontal axis BB. When thedevice is in position on a grinding machine the said rigid part 34 lieswith its front reference surface 34A in a vertical plane, the hinge axisAA lying vertically and the rocking axes of the templatefollower pin 18and the dressing-tool holder 28 lying horizontally. A template 37 issecured to the part 36 and thus to the part 35 by countersunk screws 38(Fig. 1A), the template being located accurately by means of twostraight edges 39 and 40. The axis AA is thus disposed vertical, andperpendicular to the axis of rotation C-C of the grinding Wheel 41, andparallel to the template plane. The part 35 is retained in the positionto which it has been rotated by means of two lock-nuts 42 and 43 fixedto the rigid part and frictionally engaging the part 35. A mark 44 onthe part 34 co-operates with a scale 45 fixed to the part 35 to show theangle between the planes of the template 37 and the surface 34A.

Similarly, when the device is in position on a grinding machine, theaxis B-B lies horizontally, parallel to the axis of rotation C-C of thegrinding wheel 41, and close and parallel to the plane of the templateon the side of the template support remote from the template followerpin 18. The part 36 is retained in the position to which it has beentilted by means of a lock-nut 46 fixed to the part 36 and frictionallyengaging the part 35. A scale 47 fixed to the part 34 and a pointer 56fixed to part 36 show the angle between the planes of the template 37and the surface 34A.

The template follower member is V-shaped and is constituted by the pin18, which engages the template profile, and two side wings 48 The memberis pivoted freely between a pin 49 and a rod 50, and is constrained torotate with the rod 50 without backlash by means of a pin 51 on themember engaging in a slot in an arm 52 which is rotatable with the rod50. The rod 50 is in turn rotatable with a shaft 53 on which are fixedthe drum 31 and an operators hand-wheel 54. The pin 49 is carried by asleeve 55 mounted in a forked part 16A of the lever 16, the end of thesleeve which projects beyond the part 16A being ground truly fiat andengaging the surface 34A of the part 34. Thus, the link parallelogramcannot be distorted by a careless operator pushing the lever 16 too hardin the direction towards the template support.

The length of the template-follower member, in a direction perpendicularto the plane of the surface 34A, is sufficient for its mounting in thelever 16 not to foul the template when the latter is rotated through itsgreater angle to the plane of the surface 34A. The edge forming the tipof the V-section has the same shape as the top of the dressing tool. itsradius being equal to that of the dressing-tool tip multiplied by themechanical advantage of the pantograph connection. The edge of thetemplate 37 engaged by the pin 18 is bevelled, as shown at 37 in Fig. 2,to ensure that the pin 18 will engage the correct profile and to obviateerrors in the profile produced on the grinding wheel which might be dueto the thickness of the template.

The scale 45 is graduated in degrees and minutes from zero to the valueof the maximum required helix angle of the threads to be formed (usuallyfrom zero to about 15). The scale 47 is preferably graduated in degreesfrom zero to 35. If the angle required lies between 35 and 45 degrees,the dressing tool is first displaced along its rocking axis, asmentioned above, to take account of the excess over 35, and the template37 is then tilted the full amount of the scale 47.

Two springs 56 (only one shown) are provided to take the weight of thepantograph linkage, so that the weight does not have to be supported bythe operator whilst manipulating the handle 54.

I claim:

I. A pantographic wheel dressing device for attachment to a grindingmachine and for forming on the grinding wheel thereof a profilereproduced from a template, the device comprising a base for mounting onthe grinding machine, a grinding wheel rotatably mounted on saidmachine, a template support for angularly adjustably mounting thetemplate thereon, said support comprising a first part rigid with thebase and a second part pivotally mounting the template on said firstpart about a fixed axis parallel to the axis of rotation of the grindingwheel, a first member mounted on said base, a bearing in said firstmember, a template-follower engageable with the template mounted in saidbearing and rockable about the axis thereof, a second member mounted onsaid base, a bearing in said second member, a dressing-tool holdermounted in the last-mentioned bearing and rockable about the axisthereof, a pantograph connection between said first and second members,and a connection supplementary to the said pantograph connectionconstraining the template-follower member and the dressing-tool holderto rock in unison about an axis normal to the axis of the wheel.

2. A pantographic wheel dressing device as claimed in claim 1, whereinthe said pantograph connection comprises a link parallelogram.

3. A pantographic wheel dressing device as claimed in claim 1, whereinthe said first member comprises a forked lever and two coaxial bearings,each disposed in one arm of the forked lever, and the template followerextends between and is mounted for rotation in the two coaxial bearings.

4. A pantographic wheel dressing device as claimed in claim 1, whereinthe said first part of the template support includes a reference surfaceand the template follower comprises a bearing surface engaging the saidreference surface.

5. A pantographic wheel dressing device for attachment to a grindingmachine and for forming on the grinding wheel thereof a profilereproduced from a template. the device comprising a base for mounting onthe grinding machine, a template support for adjustably mounting thetemplate thereon, the said support comprising a first part rigid withthe base and a second part for pivotally mounting the template on saidfirst part about two mutually perpendicular axes, one of said axes beingcapable of being set parallel to the axis of rotation of the grindingwheel, a first member mounted on said base, a bearing in said firstmember, a template-follower engageable with the template mounted in saidbearing and rockable about the axis thereof, a second member mounted onsaid base, a bearing in said second member, a dressingtool holdermounted in the last-mentioned bearing and rockable about the axisthereof, a pantograph connection between said first and second members,and a connection supplementary to the said pantograph connectionconstraining the template-follower member and the dressingtool holder torock in unison.

6. A pantographic wheel dressing device as claimed in claim 5, whereinthe said pantograph connection comprises a link parallelogram.

7. A pantographic wheel dressing device as claimed in claim 5, whereinthe said first member comprises a forked lever and two coaxial bearings,each disposed in one arm of the forked lever, and the template followerextends between and is mounted for rotation in the two coaxial bearings.

8. A pantographic wheel dressing device as claimed in claim 5, whereinthe said first part of the template support includes a reference surfaceand the template follower comprises a bearing surface engaging the saidreference surface.

9. A pantographic wheel dressing device for attachment to a grindingmachine and for forming on the grinding wheel thereof a profilereproduced from a template, the device comprising a base for mounting onthe grinding machine, a template support for adjustably mounting thetemplate thereon, the said support comprising a first part rigid withthe base, a second part, and a third part for mounting the template, thesecond part being pivoted to the first part about a first axis and thethird part being pivoted to the second part about a second axis mutuallyperpendicular with the first axis, one of the said axes being capable ofbeing set parallel to the axis of rotation of the grinding wheel, afirst member mounted on said base, a bearing in said first member, atemplate-follower engageable with the template mounted in said bearingand rockable about the axis thereof, a second member mounted on saidbase, a bearing in said second member, a dressing-tool holder mounted inthe last-mentioned bearing and rockable about the axis thereof, apantograph connection between said first and second members, and aconnection supplementary to the said pantograph connection constrainingthe template-follower member and the dressing-tool holder to rock inunison.

10. A pantographic wheel dressing device for attachment to a grindingmachine and for forming on the grinding wheel thereof a profilereproduced from a template, the device comprising a base for mounting onthe grinding machine, a template support for adjustably mounting thetemplate in a plane, the said support comprising a first part rigid withthe base, a second part, said second part being pivoted to the firstpart about a first axis, means for retaining the first and second partsin predetermined angular relationship relative to one another, a thirdpart for mounting the template pivoted to the second part about a secondaxis mutually perpendicular with the first axis, one of the said axesbeing capable of being set parallel to the axis of rotation of thegrinding wheel, means for retaining the second and third parts inpredetermined angular relationship relative to one another, a firstmember mounted on said base, a bearing in said first member, atemplate-follower engageable with the template mounted in said bearingand rockable about the axis thereof, a second member mounted on saidbase, a bearing in said second member, a dressing-tool holder mounted inthe last-mentioned bearing and rockable about the axis thereof, a linkparallelogram pantograph connecting the said first and second members,and a connection supplementary to the said pantograph constraining thetemplate-follower member and the dressing-tool holder to rock in unison.

References Cited in the file of this patent UNITED STATES PATENTS731,066 Nye June 16, 1903 790,172 Benton May 16, 1905 1,302,540 HansonMay 6, 1919 1,424,196 Fowler Aug. 1, 1922 1,594,607 Engelmann Aug. 3,1926 2,225,489 Tessky Dec. 17, 1940 2,452,509 Victory Oct. 26, 19482,469,844 Porter May 10, 1949 FOREIGN PATENTS 643,240 Great Britain July24, 1951

